I. Field of the Invention
This invention relates generally to tag axle systems and, more particularly, to a steerable tag axle system that enables a deployed ground engaging tag wheel to turn laterally to reduce tire wear and stress on the tag axle assembly.
II. Discussion of the Related Art
Auxiliary axle systems or tag axles are well known in the art for augmenting the load carrying capabilities of hauling vehicles. Tag axles carry a wheel which may be deployed to a ground engaging position or raised to a stowed position. The tag axle provides an additional axle to keep a loaded vehicle within legal per axle weight restrictions imposed by state or federal governments.
U.S. Pat. No. 5,090,495, issued to Ronald E. Christenson, an inventor herein, and assigned to the same assignee as the present invention, describes a tag axle system including a pair of spaced stub axles having independently operated suspension systems for lowering and raising the associated wheel. The system may be adapted to any load hauling vehicle and is well suited for use on rear unloading vehicles, such as dump trucks or refuse trucks, an example of which is a rear loading refuse truck having a rear refuse receiving hopper swept by an hydraulic compacting mechanism. In such a refuse truck, the loading trough area or tailgate hopper extends a considerable distance behind the rear axle and below the frame of the truck, as described and illustrated in U.S. Pat. No. 3,739,927, to Gollnick, the disclosure of which is hereby incorporated by reference. The stub axles of the '495 system are positioned behind the rear axle and on each side of the tailgate. In the ground engaging position, the tag axles produce a leveraging effect around the rear axle to assume some of the weight carried by the rear wheels and distribute weight to the front wheels. However, since the wheels are not steerable, excessive tire wear and stress on the associated tag axle assembly may occur as the vehicle negotiates a turn or the like.
Tag axle systems including steerable wheels have been built using conventional kingpin and tie rod turning assemblies. U.S. Pat. Nos. 4,705,133 and 4,762,421, issued to Ronald E. Christenson and Garwin B. McNeilus and assigned to the same assignee as the present invention, describe tag axle systems which are lowered from the rear of a vehicle and carry wheels on spaced stub axles pivotally attached as by kingpin turning assemblies. The wheels are held substantially away from the rear of the vehicle and a tie rod is disposed between them to maintain alignment. This steering system works well on tag axles wherein the wheels can be in direct communication without interfering with operation of the vehicle. However, where the tag axle wheels are held near the rear of a rear unloading vehicle this conventional steering system will interfere with unloading operations. Also, a conventional kingpin and tie rod assembly will interfere with the use of a low hanging tailgate, such as a tailgate hopper on a rear loading refuse truck.